The invention relates to a centrifugal pump, and a method of pumping medium consistency suspensions such as paper pulp, that is effective yet does not require the utilization of a vacuum system or the like to remove gas from the pump. The invention is particularly applicable to medium consistency finely comminuted cellulosic fibrous material suspensions (paper pulp) which have a consistency of between about 6-20%.
Many of the prior art pumps utilized for pumping paper pulp of medium consistency, have vacuum systems associated therewith, such as shown in U.S. Pat. Nos. 4,435,193, 4,410,337, and 4,273,562. Vacuum systems typically are not needed if the pumps are installed on the bottoms of high density towers or on the bottoms or sides of long chutes (e.g. 10 meters or greater). Approaches have been suggested for mechanically feeding suspension to the pump so that even where short chutes or towers or vessels are utilized it is not necessary to degas the suspension. Typical of this latter approach are U.S. Pat. Nos. 4,531,892 and 4,637,779. While such approaches can be generally successful, there are practical difficulties associated therewith, and/or the equipment is more complicated than is desired.
According to the present invention, a centrifugal pump is provided which is simple in construction yet can effectively mechanically feed the pulp to the impeller of a centrifugal pump so that a vacuum system is not necessary though the pump can be employed in short chutes, towers, or the like. This is accomplished according to the invention by providing the pump as a hollow shaft having elongated slots allowing communication between the interior and exterior thereof. Impeller blades are mounted on the shaft and extend from the inlet generally toward the outlet of the centrifugal pump. A simple self-feeding means, preferably a boat-type propeller, is mounted on the shaft for rotation with the shaft. The propeller is hollow and preferably extends exteriorly of the pump housing into the chute, tower, or other vessel with which the pump is associated. Anti-rotation means, which preferably comprise a plurality of stator vanes disposed in the vessel generally parallel to the axis of rotation, and having portions thereof defining an imaginary circle concentric with the shaft, ensure that the suspension acted upon by the propeller will be fed directly to the impeller blades, rather than merely rotating. The pump housing is open between the propeller and the impeller blades so that the suspension is fed directly from one to the other.
Utilizing the centrifugal pump according to the invention it is possible to pump medium consistency (e.g. about 6-20%) pulp or a like suspension. The method according to the invention comprises the following steps: continuously acting upon the suspension to progressively: Effect feeding of the suspension in a first dimension under the influence of a rotating element, while preventing significant rotation of the suspension during such feeding. After feeding of the suspension immediately effecting fluidization thereof so as to centrifugally pump the suspension to another location; and the steps being practiced so that degassing of the suspension is avoided. Alternatively, degassing can be accomplished without a vacuum system since the propeller pressurizes the gas and forces it out the pump.
It is the primary object of the present invention to provide for the simple yet effective self-feeding of medium consistency suspension, and subsequent centrifugal pumping thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.